Adjustment of a TiO2 suspension containing electrolytes to the isoelectric point (IEP) enabled easy separation of fine particles of TiO2 by a solids-retaining type centrifuge, which was combined with a batch photoreactor. Optimum separation conditions and reusability of the recovered TiO2 for the degradation of dibutyl phthalate (DBP) were examined. For synthesized waste water samples (5 muM DBP in tap and well water), suspended TiO2 was easily separated without addition of electrolytes after degradation of DBP.